As the relevance of ion channels as therapeutic drug targets has become accepted, and as the availability of large chemistry libraries for screening has become commonplace, the lack of functional ion channel assays has been realized as a key problem for drug discovery. This proposal addresses the development of a functional cell-based, non- radioactive channel assay for measurement of responses due to the activation or inhibition of G-protein coupled inward rectifier potassium (GIRK) channels. These channels are end-point effectors responding to the modulation of G-protein coupled receptors such as dopamine and mu opioid receptors. The channels have therapeutic potential as drug discovery targets in a variety of diseases. The assay to be developed will utilize a 96-well plate fluorescence detector coupled with mammalian cell lines expressing human cloned GIRK proteins and human cloned receptors. Initial tests of the feasibility of the screening system will be accomplished with known ligands and channel antagonists, followed by screening of a limited number of novel compounds. Ultimately, the full development of this system will provide a means for screening thousands of compounds, which activate or inhibit GIRK-dependent changes. PROPOSED COMMERCIAL APPLICATION: ICAgen is proposing to develop a functional ion channel assay which will detect the effects of molecules acting as agonists or antagonists to G-protein coupled receptor/ion channel effector pathways. This assay would be nonradioactive and useful for screening large numbers of compounds. The commercial applications of such an assay include: (1) a screening system which can be utilized on a contract basis with any pharmaceutical company wishing to assay the end- point functional effects of compounds which target receptor-G-protein coupled ion channel signal transduction pathways, (annual estimated commercial value $100,000 to $500,000, and (2) a screening system which can be utilized by ICAgen to test its libraries of compounds to identify G-protein-coupled channel antagonists and agonists for the treatment of diseases of the central nervous system (commercial value depends on stage of compound development, market share, etc.).